1. Field of the Invention
This invention relates to hermitically sealed liquid pumps. Certain types of such pumps are known as "canned pumps". It has applicability particularly to those pumps which operate from a rotating shaft, such as turbine pumps and centrifugal pumps in particular. A feature of the pump permits the elimination of a stuffing box or mechanical seal at the point where the rotating shaft enters the pump casing. This type of structure has particular advantage when pumping corrosive, explosive, low boiling point, or toxic liquids, or when pumping refrigerants or any hazardous liquid or slurry. It is useful in the fields of cryogenics and in heat transfer applications. In general, this pump sealing system is useful in applications where it is desired to avoid any leakage of the liquid being pumped.
Some advantages of this system include more stable and reliable operation than has been available before, better control of the liquid level over the pump and below the motor, the possibility of using much lighter gage and weight construction, better motor cooling, the possibility of using smaller frame size motors, and more protection against catastrophe.
2. Prior Art
Liquid sealed pumps and "canned pumps" have been known. Many patents disclose such pumps in general, or isolated portions of the system.
Prior expedients were based on the principle of balancing the pump discharge pressure with the gas pad pressure above the seal. Since pressure varies as a square of flow rate, it is almost impossible to maintain a stable level of liquid in the seal when the pump discharge pressure varies. The liquid level is very sensitive to discharge pressure variations and it was particularly difficult to control the lower liquid level without going to relatively extremely big tanks, of the order of 10-20 larger than in the present invention.
One particular structural and functional difference of the present invention over anything disclosed or suggested by the prior art is that the present invention contemplates a controlled by-pass or return from the quantity of liquid above the seal and forming a part of the liquid seal, to the pump suction. A number of important consequences flow from this concept, as have been briefly mentioned above. There are other specific improvements in the present invention over the teachings of the prior art.